Torch, ICP

SFC-ICP-MS requires rather expensive and complicated instrumental design [473,474]. Interfacing the SFC restrictor with the ICP torch follows different approaches for pSFC and cSFC [469]. Polar modifiers, however, do not have a serious deleterious effect on the ICP plasma, which enables the polarity of the mobile phase to be changed with no significant loss of sensitivity or resolution. This enables analysis of compounds which are too polar for adequate separation with pure C02 as the mobile phase. SFC is still in its infancy as far as speciation analysis of metal-containing additives is concerned. 

Ions produced in an ICP torch interfaced to a quadrupole mass spectrometer. Sample introduction by nebulizer, laser vaporization or electrical heating. 

The ICP torch provides a rich source of free atoms and ions from the elements comprising the sample. In ICP-MS, part of the sample stream from a point close to the centre of the fireball is directed to a mass spectrometer. The resulting mass spectrum can be used to identify elements from the mass numbers of the ion peaks and the peak size for quantitative analysis. Moreover, the whole spectrum can be displayed at the same time providing qualitative analysis for a wide range of elements from one display... 

The layout of an ICP-MS is shown schematically in Figure 8.17 and comprises three essential parts the ICP torch, the interface and the mass spectrometer. The ICP torch differs little from that discussed earlier and the mass spectrometer is very similar to those used for organic mass spectrometry and discussed in Chapter 9. Typically a quadrupole instrument would be used. The construction of the interface is shown in Figure 8.18 and is based on the use of a pair of water-cooled cones which divert a portion of the sample stream into the ion optics of the mass spectrometer whence the mass spectrum is produced by standard mass spectrometer operation. Some modern instruments also incorporate a so-... 

Te. Instruments based upon the use of a chemical flame as the atom reservoir have not proved to be generally successful. The introduction of the ICP torch renewed interest in atomic fluorescence and new instruments based on the ICP torch as a source of free atoms were constructed. However, these seem to have been only slightly more satisfactory than earlier instruments and have not come into widespread use. Some detection limits are included in Table 8.6. 

Figure 2.4 Schematic diagram of an ICP torch. The sample is carried into the torch by the carrier argon gas, and is ignited by radio-frequency heating from the RF coils. The tangential argon flow lifts the flame from the burner, preventing melting. The position of the detector in axial or radial mode is shown. (From Pollard et al., 2007 Fig. 3-3, by permission of Cambridge University Press.)...

Figure 14.8. On the left is a diagram and on the right is a picture of an ICP torch.

Triply hyphenated methods are not common. However, they do exist and have been used in certain applications to elicit information about soil chemistry. LC linked to ICP spectroscopy linked to MS is one example. The eluent from a liquid chromatograph is easily directed into an ICP torch and the gases from the ICP are then directed into an MS. Because the components from the LC are converted to gases in the ICP torch, they are thus easily analyzed by the MS [14]. 

FIGURE 9.18 A photograph of the ICP torch. From http //icp-oes.com. Reproduced with permission of Jobin-Yvon Horiba, France. 

Unlike a flame, in which only a very limited number of metals emit light because of the low temperature, virtually all metals present in a sample emit their line spectrum from the ICP torch. Not only does this make for a very broad application for ICP, but it also means that a given sample may undergo very rapid and simultaneous multielement analysis. With this in mind, it is interesting to consider the options for the optical path for the ICP instrument. 

To repeat a statement in our opening paragraph of this section, ICP measures the emission of light from the atomization/ionization/excitation source (ICP torch) rather than absorption of light by atoms... 

If high enough temperatures can be reached, any element can be excited to a level where it will produce emission of radiation. Such high temperatures can be achieved by using plasma emission. A schematic diagram of an inductively coupled plasma (ICP) torch is shown in Figure 6.6. 

The plasma energy recycle and conversion (PERC) process is an indirectly heated ex situ thermal recycling and conversion technology. According to the vendor, it treats hazardous waste, mixed radioactive waste, medical waste, municipal solid waste, radioactive waste, environmental restoration wastes, and incinerator ash in gaseous, hquid, slurry, or solid form. The technology uses an induction-coupled plasma (ICP) torch as its heat source coupled to a reaction chamber system to destroy hazardous materials. 

One of the first reported couplings of GC-ICP-MS was by Van Loon et al. [115], who used a coupled system for the speciation of organotin compounds. A Perkin-Elmer Sciex Elan quadrupole mass filter instrument was used as the detector with 1250 or 1500 W forward power. The GC system comprised a Chromasorb column with 8 ml min 1 Ar/2 ml min-1 02 carrier gas flow with an oven temperature of 250°C. The interface comprised a stainless-steel transfer line (0.8 m long) which connected from the GC column to the base of the ICP torch. The transfer line was heated to 250°C. Oxygen gas was injected at the midpoint of the transfer line to prevent carbon deposits in the ICP torch and on the sampler cone. Carbon deposits were found to contain tin and thus proved detrimental to analytical recoveries. Detection limits were in the range 6-16 ng Sn compared to 0.1 ng obtained by ETAAS, but the authors identified areas for future improvements in detection limits and scope of the coupled system. 

Carey and Caruso [126] also summarised the two main approaches to interfacing the SFC restrictor with the ICP torch. The first method, used with packed SFC columns, introduces the restrictor into a heated cross-flow nebuliser and the nebulised sample is subsequently swept into the torch by the nebuliser gas flow. Where capillary SFC systems are used, a second interface design is commonly employed where the restrictor is directly introduced into the central channel of the torch. This interface is more widely used with SFC-ICP-MS coupling [20]. The restrictor is passed through a heated transfer line which connects the SFC oven with the ICP torch. The restrictor is positioned so that it is flush with the inner tube of the ICP torch. This position may, however, be optimised to yield improved resolution. The connection between the transfer line and the torch connection must be heated to prevent freezing of the mobile phase eluent after decompression when exiting the restrictor. A make-up gas flow is introduced to transport the analyte to the plasma. This... 

The first instance of SFC coupled to ICP-MS was reported by Shen et al. [127] for the speciation of tetraalkyltin compounds. Liquid C02 was used as the mobile phase and the SFC column was completely inserted through the transfer line and connected to a frit restrictor (Fig. 11). The restrictor was heated to approximately 200°C by a copper tube inserted into the ICP torch. Tetramethyltin (TMT), tetrabutyltin (TBT), tetraphenyltin (TPT), tributyltin acetate... 

The basic set-up and compounds of an ICP-AES and ICP-MS are shown in Fig. 2. The ICP part is almost identical for AES and MS as detection principle. The ICP torch consists of three concentric quartz tubes, from which the outer channel is flushed with the plasma argon at a typical flow rate of 14 1 min-1. This gas flow is both the plasma and the cool gas. The middle channel transports the auxiliary argon gas flow, which is used for the shape and the axial position of the plasma. The inner channel encloses the nebulizer gas stream coming form the nebulizer / spray chamber combination. This gas stream transports the analytes into the plasma. Both the auxiliary and the nebulizer gas flow are typically around 1 1 min-1. The plasma energy is coupled inductively into the argon gas flow via two or three loops of a water-cooled copper coil. A radio frequency of 27.12 or 40.68 MHz at 1-1.5 kW is used as power source. The plasma is... 

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